Preheat the oven to 350 °F (180 °C). Line a large baking sheet with parchment paper and place the hazelnuts on it.

Roast on the medium rack for 10 minutes, remove from the oven and cool down completely - it takes about 20 minutes.

Rub the hazelnuts between your hands to peel off the skin. You want all or most of the hazelnut skins to be removed.

Add the hazelnuts to a high-speed blender, and blend them for 20 seconds, stop, scrape down the sides of the bowl with a rubber spatula, and repeat 2-3 times until it forms hazelnut flour. Don't blend for too long in one go, or it turns the nuts into hazelnut butter. It's okay if you have a few larger pieces of nuts, but not too many, as the batter wouldn't stick together and would remain loose.

Pour the ground hazelnuts into a mixing bowl and add the remaining ingredients: maple syrup and unsweetened cocoa powder.

Stir with a silicone spatula until it forms a sticky batter - it will look quite runny.

Fold in salt and chocolate chips if used. Stir to evenly incorporate.

Drop 9 dollops of batter on a large baking sheet, lined with lightly oiled parchment paper. Leave an inch of space between each. They won't expand much in the oven.

Bake the cookies for 14 minutes at 350 °F (180 °C) until the top is dry. They will be soft to the touch, that's normal. Remove from the oven and let the cookies cool down on the baking sheet at room temperature. Do not touch them for at least 20 minutes.

The cookies firm up and become chewy after they cool down on the baking sheet.